Selecting Disease Resistant Tomatoes

Auburn, April 9, 2003---If your tomato plants sickened and died last year and you are not sure why, one answer could be tomato spotted wilt virus (TSWV).  Dr. Joe Kemble, a vegetable horticulturist with the Alabama Cooperative Extension System, says there are only a limited number of varieties available that are resistant to TSWV.

“While there are many varieties that offer resistance to other diseases such as Fusarium wilt, there are only a few that possess resistance to TSWV,” says Kemble.

Kemble says home gardeners may be able to purchase one of several resistant varieties either as seeds or as transplants.  These varieties include Amelia VR (also called HMX 0800), BHN444 and BHN640. 

“Seeds should be available from certified seed dealers in the South,” says Kemble.

Bonnie Plant Farms of Union Springs is offering transplants of the BHN444 variety under the name Southern Star.  This new hybrid variety was selected specifically for its resistance to TSWV.  

Kemble says the determinate variety is a heavy fruit setter with early to mid- season maturity.

“Its fruit are globe-shaped with green shoulders. It produces large and extra large red fruit with good firmness and flavor,” says Kemble.  “In the home garden, it should be staked or caged.”

Dr. Ed Sikora, an Extension plant pathologist, says TSWV was first identified in Alabama in the mid-80s.

“The host range of TSWV extends to more than 170 species of plants, including many herbaceous ornamentals, in more than 35 plant families.  In the home garden, tomatoes, peppers, eggplant and potatoes are all vulnerable to the disease,” says Sikora.  “The disease is a particular problem for the state’s peanut growers.”

He says tomato plants infected with TSWV are stunted and often die. Initially, leaves in the terminal portion of the plant stop growing, become distorted and turn pale green.

In young leaves, veins thicken and turn purple, causing the leaves to appear bronze. Necrotic spots or ring spots frequently occur on infected leaves.  Stems of infected plants often have purplish brown streaks. Infected fruit may exhibit numerous ring spots and blotches and may become distorted if infected when immature.

“TSWV is usually spread by an insect called thrips,” says Sikora.  “Currently, there is no effective way to control TSWV, but homeowners can use some basic strategies to reduce the spread of TSWV.”

Control weeds adjacent to the field to reduce the source of infection.  The disease can overwinter in weeds.

Apply systemic insecticides to the soil at planting.  This will slow the initial spread of the virus into the field.

Spray bordering weeds and the tomato crop with insecticides to suppress thrips populations and spread of TSWV.

Remove and destroy infected plants as soon as symptoms appear.

Source:  Dr. Joe Kemble, Horticulturist, (334) 844-3050 and Dr. Ed Sikora, Plant Pathologist, (334) 844-5502, Alabama Cooperative Extension System.

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